Megatest

(define (dbfile:cautious-open-database fname init-proc #!optional (tries-left 10))
  (let* ((lock-file (conc fname".lock"))
	 (retry (lambda ()
		  (thread-sleep! 1.1)
		  (if (> tries-left 0)
		      (dbfile:cautious-open-database fname init-proc (- tries-left 1))))))
    (assert (>= tries-left 0) (conc "FATAL: Five attempts in dbfile:cautious-open-database of "fname", giving up."))
    (if (not (dbfile:simple-file-lock lock-file))
    (if (and (file-write-access? fname) (not (dbfile:simple-file-lock lock-file)))
	(begin
	  (dbfile:print-err "INFO: lock file "lock-file" exists, trying again in 1 second.")
	  (thread-sleep! 1)
	  (dbfile:cautious-open-database fname init-proc (- tries-left 1)))
	(let* ((db-exists (file-exists? fname))
	       (result (condition-case
			   (let* ((db (sqlite3:open-database fname)))

			     (retry))
			(exn (permission)(dbfile:print-err exn "ERROR: database " fname " has some permissions problem.")
			     (retry))
			(exn ()
			     (dbfile:print-err exn "ERROR: Unknown error with database " fname " message: "
					       ((condition-property-accessor 'exn 'message) exn))
			     (retry)))))
          (if (file-write-access? fname)
	  (dbfile:simple-file-release-lock lock-file)
	    (dbfile:simple-file-release-lock lock-file)
          )
	  result))))


(define (dbfile:open-no-sync-db dbpath)
  (if *no-sync-db*
      *no-sync-db*
      (begin

	  (thread-sleep! 0.25)
	  (if (file-exists? fname)
	      (handle-exceptions exn
                #f 
                (with-input-from-file fname
	  	  (lambda ()
		    (equal? key-string (read-line)))))
	      #f)))))
	      #f)
       )
    )
  )
)

(define (dbfile:simple-file-lock-and-wait fname #!key (expire-time 300))
  (let ((end-time (+ expire-time (current-seconds))))
    (let loop ((got-lock (dbfile:simple-file-lock fname expire-time: expire-time)))
      (if got-lock
	  #t
	  (if (> end-time (current-seconds))